Cracks in walls. Sticking doors and windows. Sloping floors. These signs can indicate subsidence — downward movement of the ground beneath your home’s foundations — or they can be caused by far less serious issues like thermal movement, settlement, or poor original construction. Telling the difference requires a structural engineer who understands ground behaviour and foundation design. Crown Architecture & Structural Engineering carries out structural assessments for properties with suspected subsidence across the UK. Call 07443804841 to discuss your concerns.

What Is Subsidence?

Subsidence is the downward movement of the ground beneath a building’s foundations, causing the foundations — and the building above — to move. It is distinct from:

• Settlement: Normal downward movement as a building consolidates its load into the ground after construction. Usually gradual and self-limiting.
• Heave: Upward movement of the ground, typically caused by soil swelling or tree roots being removed (which allows moisture-shrunk clay to reabsorb water and expand).
• Thermal/moisture movement: Seasonal expansion and contraction of building materials — particularly widespread in older solid brick walls — producing cracking that opens and closes with seasons.

True subsidence is usually associated with specific causes: clay soil shrinkage (particularly in dry summers), leaking drains, mining activity, or tree roots extracting moisture from clay soils.

Common Signs of Subsidence

• Diagonal cracks running from the corners of windows and doors, typically wider at one end
• Cracks that are wider at the top than the bottom (sagging) or bottom than the top (hogging)
• Cracks appearing and growing during dry summers (particularly in clay soil areas)
• Visible difference in level between sections of the property
• Doors and windows that suddenly begin sticking after years of normal operation
• Gaps appearing between walls and floors or ceilings
• Sloping floors, particularly in older properties with suspended timber floors

Not all cracking indicates subsidence. Hairline cracks at the junction of plasterboard sheets, horizontal cracking in brick courses due to failed wall ties, or fine shrinkage cracks in plasterwork are usually cosmetic. A structural engineer will categorise the cracking and assess its significance.

BRE Crack Classification

The Building Research Establishment (BRE) Digest 251 provides a standard classification system for cracks in masonry buildings:

• Category 0: Hairline — less than 0.1mm width. Negligible.
• Category 1: Fine — up to 1mm width. Not serious.
• Category 2: Slight — up to 5mm width. Easily filled; may recur.
• Category 3: Moderate — 5–15mm or several Category 2 cracks. Requires some opening up, repointing, possibly brick replacement.
• Category 4: Severe — 15–25mm. Extensive repair involving breaking out and rebuilding; doors and windows distorted.
• Category 5: Very severe — greater than 25mm. Major structural damage requiring major repair; risk of instability.

A structural engineer will classify the cracking at your property and advise on the significance and urgency of any remedial action.

What Does a Structural Subsidence Assessment Involve?

When Crown Architecture & Structural Engineering carries out a structural subsidence assessment, we typically:

1. Visual inspection: Systematic inspection of all accessible areas of the building — internal and external — noting the location, width, length, and pattern of all cracks and any other signs of movement.
2. Pattern analysis: The pattern of cracking is often diagnostic — sagging at the centre of a wall, hogging at the corners, cracking at specific weak points. The pattern helps distinguish subsidence from other causes and can identify the likely area of ground movement.
3. History review: Review of available information about the building’s history, the local geology, known drains routes, nearby trees, and any previous works to the building or its surroundings.
4. Monitoring recommendation: For active movement, crack monitoring studs are typically installed and readings taken over 3–12 months to establish whether movement is ongoing, cyclical (seasonal), or has stabilised.
5. Structural report: A written report classifying the cracking, assessing the likely cause, assessing the risk, and recommending further investigation or remedial action.

Ground Investigation for Subsidence

Where the structural assessment identifies a risk of subsidence or requires more information about the ground conditions and foundation depth, a ground investigation (trial pits or boreholes) may be recommended. Trial pits alongside the affected walls allow the foundation depth, type, and condition to be inspected, and allow soil samples to be taken for laboratory analysis. This is particularly important on clay soils where the shrink-swell behaviour of the clay needs to be understood.

Common Causes of Subsidence and Their Remedies

Clay Soil Shrinkage

Clay soils shrink in dry conditions as water is extracted, and expand when they rewet. This seasonal movement can cause cyclical cracking that is worse in dry summers. The solution varies from monitoring only (if movement is limited) through to underpinning (if foundation depths are insufficient to reach stable soil below the active zone). Trees within root-spread distance of the foundations are often a contributing factor.

Tree Roots

Large, water-hungry trees (particularly oaks, willows, and poplars) near buildings can extract significant moisture from clay soils, causing localised subsidence. The assessment must consider the species, size, age, and distance of nearby trees. Removal of problematic trees can paradoxically cause heave (as the soil reabsorbs moisture), so the timing and approach must be managed carefully with specialist advice.

Leaking Drains

Leaking drains wash away fine particles from the soil, causing voids beneath foundations. CCTV drain surveys are an important diagnostic tool where drain leakage is suspected. Drain repair and grouting of any voids are the typical remedies.

Mining Subsidence

In areas with a history of coal or other mining, ground movement from old workings can cause subsidence. The Coal Authority provides maps of historic mining activity. Coal mining subsidence damage is potentially covered by the Coal Authority’s claims process. A structural engineer with experience of mining subsidence will advise on the assessment and claims process.

Underpinning: When Is It Required?

Underpinning deepens or strengthens the foundations to bear on stable ground below the zone of movement. It is typically required where foundations are too shallow for the soil conditions, or where significant ongoing movement has been confirmed by monitoring. Underpinning is not a universal solution to subsidence — it must be preceded by identifying and addressing the cause of movement (removing the tree, repairing the drain) otherwise the underpinned section may simply move differently from the rest of the building.

Modern underpinning techniques include mass concrete underpinning (traditional, most common for residential), mini-piled underpinning (for poor access or deep movement), and resin injection (for limited applications where deep underpinning is not required).

Insurance and Subsidence

Subsidence caused by causes outside your control (shrinking clay, tree roots from a neighbour’s property, drain failure from a shared sewer) may be covered by your buildings insurance. Most standard home insurance policies include subsidence cover. If you make a subsidence claim, your insurer will typically appoint their own structural engineer — but having your own independent structural assessment first is advisable to understand the position before approaching your insurer.

Properties with a history of subsidence are harder to insure and sell. Full disclosure to prospective buyers is legally required.

Frequently Asked Questions

Can a crack in my wall just be settlement rather than subsidence?

Yes — settlement (initial consolidation after construction) is normal and usually self-limiting. A structural engineer will assess whether cracking is consistent with historic settlement or indicates ongoing movement. The key distinction is whether cracking is active (growing) or historic.

How long does a structural subsidence assessment take?

The site visit typically takes 2–4 hours depending on the size and complexity of the property. The written report is usually produced within 1–2 weeks. If crack monitoring is recommended, the monitoring period adds 3–12 months to the assessment timeline.

Do I need a structural engineer or a surveyor for subsidence?

Both RICS surveyors and structural engineers carry out subsidence assessments. A structural engineer has deeper technical expertise in analysing the structural implications and designing any required remedial works. For complex cases or where underpinning is under consideration, a structural engineer is the appropriate professional.

Will underpinning affect my property’s value or insurability?

A property that has been professionally underpinned and where the cause of movement has been addressed can be mortgaged and insured, although specialist insurance may be required. Underpinning alone (without addressing the root cause) is less reassuring to buyers and insurers. Full documentation of the cause, the underpinning design, and the subsequent monitoring is essential.

What is the difference between settlement and subsidence for insurance purposes?

Insurance policies typically cover subsidence (movement caused by ground shrinkage, drainage failure, or similar external cause) but not settlement (normal consolidation of a new building). Some policies also exclude heave. The distinction matters for claims; a structural engineer’s assessment will help establish which category applies.

Crown Architecture & Structural Engineering carries out structural subsidence assessments and designs underpinning solutions across the UK. Call 07443804841 for a fee proposal or to discuss your concerns about cracking or movement in your property.